Class 12 Biology - BIHAR
Principles of Inheritance and Variation
Principles of Inheritance and Variation forms the core of classical and molecular genetics in the Class 12 Bihar Board syllabus. This chapter explores how hereditary characters are passed from parents to offspring, building upon Gregor Mendel's groundbreaking hybridization experiments. Students will study Mendel's Laws of Inheritance, deviations from Mendelian genetics like incomplete dominance and codominance, chromosomal theory of inheritance, linkage, crossing over, and genetic disorders such as hemophilia, sickle-cell anemia, and Down syndrome. Mastering this chapter is essential for securing high marks in the BSEB board examinations, as it frequently features both objective questions and long-answer derivations.
Start Learning FreeKey Concepts
Mendel's Law of Segregation
States that allele pairs separate during gamete formation, and randomly unite at fertilization without blending.
Incomplete Dominance
A genetic scenario where neither allele is completely dominant, resulting in a blended third phenotype (e.g., pink flowers in Mirabilis jalapa).
Chromosomal Theory of Inheritance
Proposed by Sutton and Boveri, stating that chromosomes are the vehicles of genetic heredity and behave identically to Mendelian factors.
Linkage and Recombination
Linkage is the tendency of genes located close together on a chromosome to be inherited together, while recombination breaks this due to crossing over.
Pedigree Analysis
A study of family history used to trace the inheritance of specific traits or genetic disorders across generations.
Chromosomal Disorders
Disorders caused by absence, excess, or abnormal arrangement of one or more chromosomes, such as Turner's syndrome and Klinefelter's syndrome.
Important Formulas
Board Exam Info
In the Bihar (BSEB) Class 12 Biology board exam, this chapter typically carries around 6 to 8 marks. Questions usually include multiple-choice questions (MCQs), short-answer questions based on Mendel's laws or pedigree charts, and 5-mark long-answer questions requiring explanations of sex determination, chromosomal disorders, or dihybrid crosses.
Frequently Asked Questions
What is the difference between incomplete dominance and codominance?
In incomplete dominance, the heterozygous offspring shows a mixed or blended phenotype of both parents (e.g., pink color). In codominance, both alleles are expressed independently and fully in the heterozygote (e.g., AB blood group).
Why did Mendel select pea plants for his experiments?
Mendel chose garden peas because they have many distinct contrasting characters, are easy to cultivate, have a short life cycle, and naturally self-pollinate but can be easily cross-pollinated manually.
What causes Down syndrome?
Down syndrome is a genetic disorder caused by the trisomy of chromosome 21, meaning the affected individual has three copies of chromosome 21 instead of a pair due to non-disjunction during meiosis.
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